The invention discloses an inertial navigation error suppression method and system based on train motion constraints. Specifically, the inertial navigation error suppression method based on train motion constraints includes: judging whether satellite signals are shielded; if satellite signals are shielded, judging the train's maneuvering state in real time to judge whether large acceleration disturbance exists in the train; if the train is free of large acceleration disturbance, correcting an inertial navigation error model; and processing the data obtained by the corrected inertial navigationerror model with unscented kalman filter algorithm, thus obtaining optimal estimations of the train position, speed and attitude. The data obtained by the corrected inertial navigation error model are processed by unscented kalman filter algorithm, thus suppressing error divergence and ensuring the accuracy of train positioning in the case of simply relying on the inertial navigation system.